A MORE PRECISE METHOD FOR CALCULATING THE FLEXURAL VIBRATION OF PROPELLER SHAFTING

Results are given and discussed of an extensive series of laboratory modal tests investigating the flexural vibration of propeller shafting. The diameter of the model shafting was about 200 mm and the test rig represented the working of the shaft in the stern tube with various configurations of bearings and different types of liner. The liners investigated were as follows: babbit, lignum vitae, Teflon-type, and resin metal. The propeller was represented by a hub (of about 700 kg weight) fixed to the overhanging part of the tailshaft. Forcing vibrations were applied to the hub in various ways: by impact loads, by an eccentric mechanical vibrator, and by electro-magnets. The resulting natural frequencies were compared with values calculated form formulae, which are given. Generally, the tests were conducted on non-rotating shafting, but some control tests were also made on rotating shafting. Cases where the tailshaft was only in partial contact with the aftermost bearing were included in the investigation; in such cases the tailshaft rested against the after edge, or the forward edge, of the aftermost bearing. It was found that even with careful positioning of the bearing to ensure full contact, the resulting increase in the natural frequency was relatively small and that, moreover, the scatter of the experimental points was quite high. It is concluded from this that in the idealisation of the set up for calculating purposes it is sufficient to assume that the critical point of support of the shaft will be the after edge of the bearing. To widen the investigation, these results have been analysed in the light of some earlier experimental studies on the shafting of the tanker Gdynia (of the Sofiya type), and also in relation to direct flexural-vibration measurements made on board Praga-type and Sofiya-type tankers. Consideration of all the results leads to the conclusion that if certain corrections are introduced, the frequency formulae give results which are accurate within plus or minus 12%. An insight into the damping characteristics of the shafting system has also been gained from this study. In the large majority of cases the dynamic magnification coefficient was found to lie in the following ranges: For babbit liners 6--10; for lignum vitae 4--7; for Teflon-type 3--5; for resin-metal 4--7. Laboratory experiments representing the shafting of the tanker Gdynia show the dynamic magnification to be 5--8.8 in the resonance band. Order from BSRA as No. 49,095.

  • Corporate Authors:

    Mezhdunarodnaya Kniga

    Smolenskaya Sennaya Pl 32/34
    Moscow G-200,   USSR 
  • Authors:
    • Abramovich, B G
    • Merkulov, V A
  • Publication Date: 1977-10

Language

  • Russian

Media Info

  • Features: References;
  • Pagination: p. 24
  • Serial:
    • Sudostroenie
    • Issue Number: 10
    • Publisher: Mezhdunarodanya Kniga

Subject/Index Terms

Filing Info

  • Accession Number: 00182535
  • Record Type: Publication
  • Source Agency: British Ship Research Association
  • Files: TRIS
  • Created Date: Oct 12 1978 12:00AM